A variety of processes and furnaces are known in which ferrous metal scrap is premelted, such as in an open hearth in the presence of, or with the introduction of oxygen or oxygen-enriched air or other gases, in order to reduce the carbon content of or otherwise refine the molten metal such as steel in association with a slag.
Reference is made to U.S. Pat. No. 2,080,625 in which scrap metal is melted in a cupola or similar furnace and then flowed into one or more secondary furnaces into which tuyere members introduce burning gas jets to swirl the molten mass while desulphurizing chemicals are introduced for refining purposes. Slag is blown out of the furnace.
Reference is also made to U.S. Pat. No. 3,689,250 which discloses an electric arc steelmelting furnace in which the disadvantages of arc melting, i.e., localized heating, poor heat transfer and direct exposure of the furnace walls to the radiation of the arcs, are reduced by introducing air-blown pellets radially against the surface of the slag to cause the slag to move into the area of the electric arcs in an attempt to keep the electrodes submerged. Among other disadvantages of such duplex processes is the fact that the air jets cool the slag, reduce the efficiency of the system and require further energy input.
Reference is also made to U.S. Pat. Nos. 3,603,571 and 4,021,192 which disclose furnaces which employ recovered heat for the preheating of metal scrap and for other purposes which improve the efficiency of the systems.
While the known steelmelting processes and furnaces involving the use of slag offer many advantages, they also present many disadvantages with respect to efficiency, energy recovery, loss of steel through oxidation, energy-input requirements, arc-damage to furnace walls, loss of electric power and/or other disadvantages.
Some of these disadvantages are overcome by the use of natural gas and/or other caloric gases as the heat source, and it is the objective of the present invention to provide a gas-fired melting process and apparatus for ferrous metal, such as steel, which can be run continuously for greatest efficiency, which provides efficient heat transfer to the solid metal scrap pieces by means of molten slag to cause the uniform melting of the metal while it is protected against oxidation and other undesirable reactions, and which permits recovery of heat for preheating of the scrap and/or to perform other useful functions which further increase the efficiency of the present process and apparatus.